diff --git a/hw/char/sifive_uart.c b/hw/char/sifive_uart.c
index 9bc697a67b..138c31fcab 100644
--- a/hw/char/sifive_uart.c
+++ b/hw/char/sifive_uart.c
@@ -35,16 +35,17 @@
  */
 
 /* Returns the state of the IP (interrupt pending) register */
-static uint64_t sifive_uart_ip(SiFiveUARTState *s)
+static uint32_t sifive_uart_ip(SiFiveUARTState *s)
 {
-    uint64_t ret = 0;
+    uint32_t ret = 0;
 
-    uint64_t txcnt = SIFIVE_UART_GET_TXCNT(s->txctrl);
-    uint64_t rxcnt = SIFIVE_UART_GET_RXCNT(s->rxctrl);
+    uint32_t txcnt = SIFIVE_UART_GET_TXCNT(s->txctrl);
+    uint32_t rxcnt = SIFIVE_UART_GET_RXCNT(s->rxctrl);
 
-    if (txcnt != 0) {
+    if (fifo8_num_used(&s->tx_fifo) < txcnt) {
         ret |= SIFIVE_UART_IP_TXWM;
     }
+
     if (s->rx_fifo_len > rxcnt) {
         ret |= SIFIVE_UART_IP_RXWM;
     }
@@ -55,15 +56,14 @@ static uint64_t sifive_uart_ip(SiFiveUARTState *s)
 static void sifive_uart_update_irq(SiFiveUARTState *s)
 {
     int cond = 0;
-    if ((s->ie & SIFIVE_UART_IE_TXWM) ||
-        ((s->ie & SIFIVE_UART_IE_RXWM) && s->rx_fifo_len)) {
+    uint32_t ip = sifive_uart_ip(s);
+
+    if (((ip & SIFIVE_UART_IP_TXWM) && (s->ie & SIFIVE_UART_IE_TXWM)) ||
+        ((ip & SIFIVE_UART_IP_RXWM) && (s->ie & SIFIVE_UART_IE_RXWM))) {
         cond = 1;
     }
-    if (cond) {
-        qemu_irq_raise(s->irq);
-    } else {
-        qemu_irq_lower(s->irq);
-    }
+
+    qemu_set_irq(s->irq, cond);
 }
 
 static gboolean sifive_uart_xmit(void *do_not_use, GIOCondition cond,